JP2023127447A - Lighting device and lighting fixture - Google Patents

Abstract

To obtain a lighting device and a lighting fixture capable of setting an appropriate switching frequency.SOLUTION: A lighting device according to the present disclosure includes: a lighting circuit which turns on a light source by turning a switching element on and off; and a control circuit which controls the lighting circuit. When a first frequency of the switching element calculated by a first arithmetic expression is outside a predetermined range, the control circuit allows the switching element to operate at the first frequency, and when the first frequency is within the range and a second frequency of the switching element calculated by a second arithmetic expression is outside the range, the control circuit allows the switching element to operate at the second frequency, a calculation result of the second arithmetic expression being smaller than that of the first arithmetic expression.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to lighting devices and lighting fixtures.

Patent Document 1 discloses a switching power supply device that obtains a predetermined output voltage by rectifying and smoothing a voltage obtained by switching a DC input voltage through a series circuit of a reactor and a switching element. This switching power supply device includes an off-time calculation section, a calculation section, and a control section. The off-time calculating section calculates the off-time of the switching element based on the on-time of the switching element calculated based on the output voltage and the reference value, the DC input voltage, and the output voltage. The calculation unit calculates at least one of the period and the frequency based on the off time and on time calculated by the off time calculation unit. The control unit controls the switching element based on a comparison result between one of the period and the frequency and one of the reference period and the reference frequency. The control unit limits the maximum frequency of the switching element and extends the off time of the switching element when the frequency exceeds the reference frequency. The control unit uses calculation to predict the bottom when the voltage across the switching element undergoes damped oscillation when the switching element is turned off, and if the frequency calculated by the calculation unit exceeds the reference frequency, the control unit calculates the bottom at least once from the predicted first bottom. Skip and turn on the switching element when the next bottom occurs.

Patent No. 6702112

A switching circuit consisting of a coil and a switching element may be used to supply power to a load such as an LED. In such a lighting device, for example, an AC input voltage is rectified by a rectifier, and the rectified voltage is boosted to become a DC voltage. This DC voltage is stepped down to obtain a predetermined voltage and is supplied to a load such as an LED. The main components of the lighting device include, for example, a rectifier circuit, a PFC circuit, and a buck converter circuit.

The frequency of the switching circuit is calculated from parameters such as the input voltage of the lighting device, the power supplied to the load, and the inductance of the coil. Generally, when the load is high, the switching frequency becomes low, and when the load is light, the switching frequency becomes high. When the switching frequency is high, the loss of the switching element tends to increase. In Patent Document 1, loss is suppressed by limiting the maximum frequency.

Furthermore, for example, according to CISPR15, it is required to satisfy standard values even when the frequency is low. In CISPR15, the lower the frequency, the more relaxed the standard value is. However, the standard value is not proportional to frequency. The standard value is a stepwise value divided by frequency. The standard value changes in proportion to, for example, 110 dB at 9 kHz or more and less than 50 kHz, and 90 dB to 80 dB at 50 kHz or more and less than 150 kHz. When the load is high, the switching frequency becomes low, and the operating frequency may become noise and be output to the outside. For example, if the switching frequency is 50 kHz, a strict standard value of 90 dB is applied. For this reason, it may be desirable to operate at a frequency below 50 kHz, at which the standard value is relaxed.

Here, control using bottom skip as in Patent Document 1 is effective control when the frequency is high. However, when the frequency is low, the frequency fluctuates greatly with one bottom skip, making detailed control impossible. Furthermore, as the number of bottom skips increases, the damped vibration may become noise and affect the outside. Therefore, noise suppression may become difficult.

The present disclosure has been made to solve the above-mentioned problems, and aims to provide a lighting device and a lighting fixture that can set an appropriate switching frequency.

A lighting device according to the present disclosure includes a lighting circuit that lights up a light source by turning on and off a switching element, and a control circuit that controls the lighting circuit, and the control circuit includes a lighting circuit that controls the switching element calculated using a first arithmetic expression. If the first frequency of the switching element is outside the predetermined range, the switching element is operated at the first frequency, and the first frequency of the switching element is within the range and the first frequency of the switching element is calculated using the second arithmetic expression. When the two frequencies are outside the range, the switching element is operated at the second frequency, and the second calculation formula has a smaller calculation result than the first calculation formula.

In the lighting device according to the present disclosure, the control circuit operates the switching element at the first frequency when the first frequency calculated by the first arithmetic expression is outside a predetermined range. In addition, if the first frequency is within the range and the second frequency of the switching element calculated by the second calculation formula, which has a smaller calculation result than the first calculation formula, is outside the range, the control circuit controls Operate the switching element. This allows an appropriate switching frequency to be set.

1 is a circuit block diagram of a lighting fixture according to Embodiment 1. FIG. FIG. 7 is a diagram showing a change in coil current over time when the boost chopper circuit according to the first embodiment operates based on a first arithmetic expression. FIG. 7 is a diagram showing a change in coil current over time when the boost chopper circuit according to the first embodiment operates based on a second arithmetic expression. FIG. 6 is a diagram illustrating the noise terminal voltage when the lighting fixture according to the first embodiment operates based on the first arithmetic expression. FIG. 6 is a diagram illustrating the noise terminal voltage when the lighting fixture according to the first embodiment operates based on the second arithmetic expression.

A lighting device and a lighting fixture according to this embodiment will be described with reference to the drawings. Identical or corresponding components may be given the same reference numerals and repeated descriptions may be omitted.

Embodiment 1.
FIG. 1 is a circuit block diagram of a lighting fixture 100 according to the first embodiment. The lighting fixture 100 includes a lighting device 10 and a light source 40. The lighting device 10 includes a lighting circuit that lights the light source 40 by turning on and off switching elements Q1 and Q2, and a control circuit 30 that controls the lighting circuit. The light source 40 includes a plurality of LEDs connected in series. A plurality of LEDs may be connected in parallel or in series and parallel. The light source 40 may include other light emitting elements such as organic EL instead of LEDs.

The lighting circuit includes a rectifier DB that rectifies commercial power supply AC, a boost chopper circuit 12, and a buck converter circuit 20. The boost chopper circuit 12 converts the pulsating voltage that has been full-wave rectified by the rectifier DB, and charges the capacitor C2 with a predetermined DC high voltage. The boost chopper circuit 12 includes a coil L1, a switching element Q1, and a diode D1. The switching element Q1 is, for example, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The voltage charged in the capacitor C2 is input to the P1 terminal of the control circuit 30 by resistor voltage division by resistors R5 and R6. This allows the control circuit 30 to detect a voltage proportional to the voltage of the capacitor C2.

The control circuit 30 performs feedback control so that the voltage charged in the capacitor C2 becomes a predetermined DC voltage, that is, so that the voltage at the P1 terminal of the control circuit 30 becomes a constant voltage. The control circuit 30 outputs a switching signal for operating the switching element Q1 from the Vg1 terminal. Generally, the operating power supply voltage of a microcomputer is lower than the driving voltage of a MOSFET. For this reason, a switching signal is once input to the MOSFET driver 18 from the Vg1 terminal of the control circuit 30. MOSFET driver 18 can output a higher voltage than control circuit 30. Therefore, the switching element Q1 can be switched stably.

A detection resistor (not shown) is connected to the source terminal of the switching element Q1, and the voltage of this detection resistor is input to the control circuit 30. The current value of the switching element Q1 can be detected by converting the current flowing when the switching element Q1 is turned on into a voltage using a detection resistor.

The boost chopper circuit 12 operates as a power factor correction circuit that increases the power factor output from the commercial power supply AC. In the power factor correction circuit operation, the on-width of the switching element Q1 is controlled to be constant in the cycle of the commercial power supply AC. Thereby, the average value of the switching current is proportional to the phase of the commercial power supply AC. At this time, the feedback period needs to be slower than the period in which the commercial power supply AC is full-wave rectified.

Further, the voltage that has been full-wave rectified by the rectifier DB is smoothed by the capacitor C1, and serves as a power source for operating the boost chopper circuit 12. The voltage generated in the capacitor C1 becomes a full-wave rectified voltage due to the operation of the boost chopper circuit 12.

Buck converter circuit 20 converts the voltage of capacitor C2 to turn on light source 40. Buck converter circuit 20 is comprised of switching element Q2, coil L2, and diode D2. The switching element Q2 is, for example, a MOSFET. The high frequency voltage output by the buck converter circuit 20 is smoothed by a capacitor C3 connected in parallel with the light source 40. As a result, a DC voltage is supplied to the light source 40.

A resistor R4 is connected to the capacitor C3 and the light source 40. A switching current output from the buck converter circuit 20 flows through the resistor R4. The current flowing through the resistor R4 is converted into a voltage and input to the P2 terminal of the control circuit 30. The current flowing through resistor R4 is a buck converter current, and its average value is equal to the LED current flowing through light source 40. The control circuit 30 outputs a switching signal for operating the switching element Q2 from the Vg2 terminal so that the voltage generated across the resistor R4 is constant. Therefore, the light source 40 is turned on by constant current control. A switching signal from the Vg2 terminal of the control circuit 30 is input to the switching element Q2 via the MOSFET driver 18, similarly to the boost chopper circuit 12. Thereby, the switching element Q2 can be switched stably.

The charge stored in the capacitor C2 is converted by the control power supply circuit section 14, smoothed by the capacitor C4, and supplied as control power to the MOSFET driver 18. The voltage of this control power source is assumed to be V1. For example, V1 is 15V. Furthermore, the voltage V1 is inputted to the VDD terminal of the control circuit 30 via the step-down circuit section 16, and serves as a control power source for the control circuit 30. The voltage at the VDD terminal is, for example, 5V. The control power supply circuit section 14 may be a step-down converter circuit such as a buck converter circuit, or may be a step-up/down converter circuit such as a flyback circuit.

Resistors R1 and R2 are connected to the capacitor C1. The voltage divided by the resistors R1 and R2 is input to the P3 terminal of the control circuit 30. In this way, the control circuit 30 detects the voltage of the commercial power supply AC and reflects it in the control.

The control circuit 30 is an IC (Integrated Circuit), a microcomputer, or the like. The control circuit 30 includes an operation parameter setting section 32 and a calculation section 34. The operating parameter setting section 32 sets the output voltage and LED current of the boost chopper circuit 12. The calculation unit 34 calculates the operating frequencies of the boost chopper circuit 12 and the buck converter circuit 20 based on the operating parameters set by the operating parameter setting unit 32.

Next, control of the switching frequency of the boost chopper circuit 12 will be explained. The control circuit 30 of the present embodiment operates the switching element Q1 at the first frequency when the first frequency of the switching element Q1 calculated by a first arithmetic expression described later is smaller than a predetermined value. Moreover, the control circuit 30 operates the switching element at the second frequency when the first frequency is higher than the specified value and the second frequency of the switching element Q1 calculated by the second arithmetic expression is smaller than the specified value. The predetermined value is, for example, 50 kHz, which is the boundary of the CISPR15 standard value.

FIG. 2 is a diagram showing a change in coil current over time when the boost chopper circuit 12 according to the first embodiment operates based on the first arithmetic expression. In the state shown in FIG. 2, the boost chopper circuit 12 is operating in critical mode. At this time, the current when the switching element Q1 is on is expressed by equation (1). Further, the current when the switching element Q1 is off is expressed by equation (2).
IL1P=Vin1×Ton1/L1...Formula (1)
IL1P=(Vout1-Vin1)×Toff1/L1...Formula (2)

Here, IL1P is the peak value of the current of the coil L1, Vin1 is the input voltage of the boost chopper circuit 12, Vout1 is the output voltage of the boost chopper circuit, Ton1 is the on time of Q1, Toff1 is the off time of Q1, and L1 is the coil L1 is the inductance value of

From equations (1) and (2), the operating frequency f1 is expressed by equation (3).
f1=1/(Ton1+Toff1)
=1/((L1×IL1P/Vin1)+(L1×IL1P/(Vout1-Vin1)))...Formula (3)

L1 is a value determined by design, and Vin1 can be detected at the P3 terminal of the control circuit 30. Further, Vout1 can be detected by the P1 terminal of the control circuit 30, and IL1P can be detected by the above-mentioned detection resistor. Further, the detected value of IL1P is determined by the power output by the boost chopper circuit 12, that is, the power approximately consumed by the light source 40. By calculating these detected values, the operating frequency f1 can be calculated. Note that changing IL1P means changing the on time of switching element Q1.

The control circuit 30 operates the switching element Q1 at the operating frequency f1 obtained from the equation (3) when the operating frequency f1 is less than the specified value of 50 kHz as a result of calculation using the equation (3). Equation (3) corresponds to the first arithmetic expression. Further, the operating frequency f1 obtained from equation (3) corresponds to the first frequency of the switching element Q1 calculated using the first arithmetic equation.

Next, a case where the operating frequency f1 obtained by equation (3) is 50 kHz or more and less than 150 kHz will be described. FIG. 3 is a diagram showing a change in coil current over time when the boost chopper circuit 12 according to the first embodiment operates based on the second arithmetic expression. In the state shown in FIG. 3, the control circuit 30 delays the timing at which the switching element Q1 is turned on by a predetermined delay time Td1.

At this time, the operating frequency f1 is expressed by equation (4).
f1=1/(Ton1+Toff1+Td1)
=1/((L1×IL1P/Vin1)+(L1×IL1P/(Vout1-Vin1))+Td1)...Formula (4)

Here, the delay time Td1 is the pause time of Q1. In other words, the delay time Td1 is the time from when the switching element Q1 is turned off and the current in the coil L1 of the boost chopper circuit 12 becomes zero until the switching element Q1 is turned on next time.

The calculation result of equation (4) is smaller than that of equation (3). In Equation (4), the predetermined delay time Td1 of the timing at which the switching element Q1 is turned on is included, so that the calculated result is smaller than that in Equation (3).

If the operating frequency f1 is less than the specified value of 50 kHz as a result of calculation using equation (4), the control circuit 30 operates the switching element Q1 at the operating frequency f1 obtained using equation (4). Note that equation (4) corresponds to the second calculation equation. Further, the operating frequency f1 obtained from equation (4) corresponds to the second frequency of the switching element Q1 calculated using the second arithmetic equation. The timing at which the switching element Q1 turns on is delayed by a predetermined delay time Td1 when operating at the second frequency than when operating at the first frequency.

If the operating frequency f1 obtained by equation (4) is 50 kHz or more, the delay time Td1 of equation (4) is increased and the operating frequency f1 is calculated again. For example, the operating frequency f1 is calculated by further adding Td1 to the delay time Td1 in equation (4). In this way, the calculation is repeated until the operating frequency f1 becomes less than 50 kHz.

As described above, in this embodiment, an appropriate switching frequency can be set by using the first arithmetic expression and the second arithmetic expression whose calculation result is smaller than the first arithmetic expression. Thereby, regardless of the input voltage, the state of the light source 40, the inductance, etc., it is possible to prevent the switching element Q1 from operating at around 50 kHz, for example. Therefore, the CISPR15 standard can be easily satisfied. Further, by setting the delay time Td1, the switching frequency can be finely controlled.

Note that the input voltage of the boost chopper circuit 12 is an alternating current voltage. Therefore, during critical mode operation, Toff1 changes depending on the phase as shown in equation (5).
Toff1=L1×IL1P×sinθ/((Vout1−(Vin1×sinθ))...Equation (5)

The off time is longest when sin θ=90°, and the off time is shortest when sin θ=0°. Therefore, in the boost chopper circuit 12, it is preferable to calculate the operating frequency f1 at which sin θ=0°, which is the highest frequency. For example, if the operating frequency f1 at sin θ=0° is 50 kHz or more and less than 150 kHz, as shown in equation (4), the timing of turning on is delayed by the delay time Td1 so that the operating frequency f1 becomes less than 50 kHz.

Next, control of the switching frequency of the buck converter circuit 20 will be explained. Similarly to the boost chopper circuit 12, the current when the switching element Q2 is on is expressed by equation (6), and the current when it is off is expressed by equation (7).
IL2P=(Vin2-Vout2)×Ton2/L2...Formula (6)
IL2P=Vout2×Toff2/L2...Formula (7)

Here, IL2P is the peak value of the current in the coil L2, Vin2 is the input voltage of the buck converter circuit 20, Vout2 is the output voltage of the buck converter circuit 20, Ton2 is the on time of Q2, Toff2 is the off time of Q2, and L2 is the coil This is the inductance value of L2.

The operating frequency f2 is expressed by equation (8) from equations (6) and (7).
f2=1/(Ton2+Toff2)
=1/((L2×IL2P/(Vin2-Vout2))+(L2×IL2P/Vout2))...Formula (8)

L2 is a value determined by design, and Vin2 can be detected at the P1 terminal of the control circuit 30. Further, IL2P can be detected at the P2 terminal of the control circuit 30. Vout2 is the voltage of the connected light source 40 and is determined by design. Further, the detected value of IL2P is determined by the target current flowing through the light source 40. By calculating these detected values, the operating frequency f2 can be calculated. Note that changing IL2P means changing the on time of switching element Q2.

If the result of calculation using equation (8) is, for example, less than 50 kHz, which is the boundary of the standard value of CISPR15, switching element Q2 is operated at the operating frequency f2 calculated using equation (8). Equation (8) corresponds to the first arithmetic expression. Furthermore, the operating frequency f2 obtained from equation (8) corresponds to the first frequency of the switching element Q2 calculated using the first arithmetic equation.

If the operating frequency f2 calculated by equation (8) is 50 kHz or more and less than 150 kHz, as in the case of the boost chopper circuit 12, equation (9) in which the timing at which switching element Q2 is turned on is delayed by delay time Td2 is used. Calculate the operating frequency f2.

f2=1/(Ton2+Toff2+Td2)
=1/((L2×IL2P/(Vin2-Vout2))+(L2×IL2P/Vout2)+Td2) ...Formula (9)

Here, the delay time Td2 is the pause time of Q2. In other words, the delay time Td2 is the time from when the switching element Q2 is turned off and the current in the coil L2 of the buck converter circuit 20 becomes zero until the switching element Q2 is turned on next time.

The control circuit 30 operates the switching element Q2 at the operating frequency f2 obtained from the equation (9) when the operating frequency f2 is less than the specified value of 50 kHz as a result of calculation using the equation (9). Note that equation (9) corresponds to the second calculation equation. Further, the operating frequency f2 obtained by equation (9) corresponds to the second frequency of the switching element Q2 calculated by the second arithmetic equation. The timing at which the switching element Q2 turns on is delayed by a predetermined delay time Td2 when operating at the second frequency than when operating at the first frequency.

If the operating frequency f2 obtained by equation (9) is 50 kHz or more, the delay time Td2 of equation (9) is increased and the operating frequency f2 is calculated again. For example, the operating frequency f2 is calculated by further adding Td2 to the delay time Td2 in equation (9). In this way, the calculation is repeated until the operating frequency f2 becomes less than 50 kHz.

From the above, in the buck converter circuit 20 as well, an appropriate switching frequency can be set by using the first arithmetic expression and the second arithmetic expression whose calculation result is smaller than the first arithmetic expression. This makes it possible to prevent the switching element Q2 from operating at around 50 kHz, for example, regardless of the input voltage, load condition, and inductance. Therefore, the CISPR15 standard can be easily satisfied.

Note that the operation parameter setting section 32 of the control circuit 30 acquires and holds various parameters in the first arithmetic expression and the second arithmetic expression. The calculation unit 34 calculates the first frequency and the second frequency based on various parameters, the first calculation formula, and the second calculation formula. The functions of the operating parameter setting section 32 and the calculation section 34 can be realized by, for example, a processor and a memory.

FIG. 4 is a diagram illustrating the noise terminal voltage when the lighting fixture 100 according to the first embodiment operates based on the first arithmetic expression. FIG. 5 is a diagram illustrating the noise terminal voltage when the lighting fixture 100 according to the first embodiment operates based on the second arithmetic expression. By using the frequency calculated by the second calculation formula, the switching frequency becomes lower than when the frequency calculated by the first calculation formula is used. Therefore, the lighting fixture 100 can be easily made to comply with noise standards without lowering the noise level.

In this embodiment, an example in which the specified value is 50 kHz has been described. The specified value is not limited to this, and may be 150 kHz or the like. The control circuit 30 may determine the switching frequency of the switching element by comparing an arbitrary range with the calculated operating frequency. That is, the control circuit 30 operates the switching element at the first frequency when the first frequency is outside the predetermined range, and operates the switching element at the first frequency when the first frequency is within the range and the second frequency is outside the range. It is sufficient to operate the switching element at two frequencies.

Further, if the operating frequencies of the boost chopper circuit 12 and the buck converter circuit 20 match, the noise level may increase. In this case, it is preferable to further increase the delay time Td and change the frequency in one of the circuits. This allows the noise level to be lowered.

Note that the technical features described in this embodiment may be used in combination as appropriate.

10 lighting device, 12 boost chopper circuit, 14 control power supply circuit section, 16 step-down circuit section, 18 MOSFET driver, 20 buck converter circuit, 30 control circuit, 32 operating parameter setting section, 34 calculation section, 40 light source, 100 lighting fixture, AC commercial power supply, C1, C2, C3, C4 capacitor, D1, D2 diode, DB rectifier, L1, L2 coil, Q1, Q2 switching element, R1, R2, R4, R5, R6 resistor

Claims (6)

a lighting circuit that lights up a light source by turning on and off a switching element;
a control circuit that controls the lighting circuit;
Equipped with
The control circuit operates the switching element at the first frequency when the first frequency of the switching element calculated by the first arithmetic expression is outside the predetermined range, and the control circuit operates the switching element at the first frequency when the first frequency is within the range. If the second frequency of the switching element calculated by the second arithmetic expression is outside the range, the switching element is operated at the second frequency, and the second arithmetic expression is calculated from the first arithmetic expression. A lighting device characterized in that the calculated result is small. The control circuit operates the switching element at the first frequency when the first frequency is smaller than a predetermined value, and when the first frequency is larger than the predetermined value and the second frequency is lower than the predetermined value. The lighting device according to claim 1, wherein the switching element is operated at the second frequency when the frequency is smaller than the value. 3. The second arithmetic expression includes a predetermined delay time for the timing at which the switching element turns on, so that the calculated result is smaller than that of the first arithmetic expression. The lighting device described. Any one of claims 1 to 3, wherein the timing at which the switching element turns on is later than when operating at the first frequency by a predetermined delay time when operating at the second frequency. The lighting device according to item 1. 4. The delay time is the time from when the switching element is turned off and the current in a coil included in the lighting circuit becomes zero until the switching element is turned on next time. The lighting device described in . The lighting device according to any one of claims 1 to 5,
the light source;
A lighting fixture comprising:

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